Polymer- and Ionic Liquid-Containing Palladium: Recoverable Soluble Cross-Coupling Catalysts

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Synthesis, properties and catalysis of quantum dots in C–C and C-heteroatom bond formations

Luminescent quantum dots (QDs) represent a new form of carbon nanomaterials which have gained widespread attention in recent years, especially in the area of chemical sensing, bioimaging, nanomedicine, solar cells, light-emitting diode (LED), and electrocatalysis. Their extremely small size renders some unusual properties such as quantum confinement effects, good surface binding properties, high surface‐to‐volume ratios, broad and intense absorption spectra in the visible region, optical and electronic properties different from those of bulk materials. Apart from, during the past few years, QDs offer new and versatile ways to serve as photocatalysts in organic synthesis. Quantum dots (QD) have band gaps that could be nicely controlled by a number of factors in a complicated way, mentioned in the article. Processing, structure, properties and applications are also reviewed for semiconducting quantum dots. Overall, this review aims to summarize the recent innovative applications of QD or its modified nanohybrid as efficient, robust, photoassisted redox catalysts in C–C and C-heteroatom bond forming reactions. The recent structural modifications of QD or its core structure in the development of new synthetic methodologies are also highlighted. Following a primer on the structure, properties, and bio-functionalization of QDs, herein selected examples of QD as a recoverable sustainable nanocatalyst in various green media are embodied for future reference.

Diindolylamine Preparation and Stability Investigations

The synthesis of diindolylamines via the palladium-catalyzed cross-coupling of aminoindoles and bromoindoles has been investigated, and efficient coupling conditions using BrettPhos, Pd(OAc)₂, K₂CO₃, and tBuOH have been identified. The diindolylamines were found to be unstable in ambient conditions. Blocking the reactive 3-position of the bromoindole coupling partner with a tert-butyl group results in a diindolylamine with improved air stability. NMR, CV, and UV-vis studies on an asymmetrically substituted 3-tert-butyl-3'H-diindolylamine indicate that the instability of the diindolylamine substrates is likely due to oxidative oligomerization. Literature conditions used for the preparation of 3-tert-butylindoles afforded only the indole tetramer. The presence of water during the alkylation reaction was identified as the cause of the formation of the tetramer. Replacing hygroscopic tBuOH with nonhygroscopic tBuCl as the alkylating reagent provided access to 7-bromo-3-tert-butyl indole.

A Co–Cu bimetallic magnetic nanocatalyst with synergistic and bifunctional performance for the base-free Suzuki, Sonogashira, and C–N cross-coupling reactions in water

A novel bimetallic catalytic system based on Cu/Co has been developed and used as an efficient, eco-friendly, and recyclable catalyst for base- and Pd-free Sonogashira, Suzuki and C–N cross-coupling reactions in mild reaction conditions.

Recent Advances Utilized in the Recycling of Homogeneous Catalysis

Homogeneous catalysts often show high activity and selectivity towards the various chemical transformations. Most of the transition metal-based active catalysts are expensive, rare, and have strict regulations for their use in pharmaceutical products. Hence, there is a requirement to develop suitable technologies for the practical separation and recycling of metal complex catalysts along with the sustainability of the process. This review focuses on the recent techniques used for the catalyst separation, their recovery, and recyclability of the homogeneous form of catalysts based on their economic compatibility and industrial applications. Various homogeneous catalysts have been reviewed on the basis of their support or media, active centres and recyclability aspects of the catalysts. This review gives brief insights into the varied examples of different recycling techniques utilized in the past 6-7 years.

Palladium stabilized on poly and mono sulfonamide ligands as novel, simple, effective, and recyclable nano catalysts for C–C cross-coupling reactions

Poly and mono sulfonamide ligands were successfully used for the stabilization of palladium nanoparticles. The prepared nano catalysts that appeared to be heterogeneous and novel were characterized with various analytical tools. To establish the catalytic activity of the prepared catalysts, they were used in the Suzuki–Miyaura and Sonogashira–Hagihara coupling reactions of aryl halides under low palladium loading conditions. The catalysts showed good stability and could be recovered and reused for seven reaction cycles without significant loss of catalytic activity.

Hybrid single-chain nanoparticles via the metal induced crosslinking of N-donor functionalized polymer chains

A set of single-chain nanoparticles was prepared via the intramolecular crosslinking of functionalized copolymers with various metal salts.

Active sites on graphene-based materials as metal-free catalysts

Defects, periphery, heteroatoms and heterojunctions can make graphene behave as a catalyst without the need for metallic elements.

Palladium nanoparticles stabilised by cinchona-based alkaloids in glycerol: efficient catalysts for surface assisted processes

Cinchona-based alkaloids led to well-dispersed palladium nanoparticles in neat glycerol, leading to efficient eco-friendly catalytic phases in hydrogenations and hydrodehalogenations.

Palladium supported on phosphinite functionalized Fe3O4 nanoparticles as a new magnetically separable catalyst for Suzuki–Miyaura coupling reactions in aqueous media

Novel phosphinite functionalized magnetic (Fe₃O₄) nanoparticles having silica nanoshells containing an imidazolium ionic liquid moiety have been successfully synthesized and used as a support and stabilizer for palladium nanoparticles.

Metal–organic frameworks catalyzed C–C and C–heteroatom coupling reactions

This critical review aims to illustrate the recent developments in the field of C–C and C–X (X = O, N) coupling reactions promoted by metal–organic frameworks.

Soluble polymer-supported hindered phosphine ligands for palladium-catalyzed aryl amination

Two structurally different heptane soluble polymers – polyisobutylene and poly(4-alkylstyrene) – are shown to be good supports for hindered biaryldicyclohexyl phosphine Pd(0) aryl amination catalysts.

A novel polymer containing phosphorus–nitrogen ligands for stabilization of palladium nanoparticles: an efficient and recyclable catalyst for Suzuki and Sonogashira reactions in neat water

Highly monodispersed palladium nanoparticles supported on polymer containing phosphorus and nitrogen ligands was successfully synthesized, characterized and used in Suzuki and Sonogashira coupling reactions in water.

Sulfasalazine in ionic liquid form with improved solubility and exposure

An ionic liquid form of sulfasalazine demonstrates improved solubility (4000×), bioavailability (2.5×), andin vivoexposure over the neutral drug.

A mechanistic study of cross-coupling reactions catalyzed by palladium nanoparticles supported on polyaniline nanofibers

Pd/PANI nanocomposites effect C–C coupling reactions mainly through a homogeneous mechanism.

Palladium nanoparticles encapsulated inside the pores of a metal–organic framework as a highly active catalyst for carbon–carbon cross-coupling

Palladium nanoparticles were successfully encapsulated in the cages of MIL-101, which exhibited high catalytic activity toward the C–C coupling reactions.